Petrogenesis of amphibole-rich ultramafic rocks in the Hida metamorphic complex, Japan: Its role in arc crust differentiation
Petrogenesis of amphibole-rich ultramafic rocks in the Hida metamorphic complex, Japan: Its role in arc crust differentiation
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DOI：
10.1016/j.lithos.2021.106440
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发表时间：
2021-12
期刊：
影响因子：
3.5
通讯作者：
K. Itano;T. Morishita;I. Nishio;J. Guotana;Yohei Ogusu;O. Ishizuka;Akihiro Tamura
中科院分区：
文献类型：
--
作者：
K. Itano;T. Morishita;I. Nishio;J. Guotana;Yohei Ogusu;O. Ishizuka;Akihiro Tamura
角闪石通过分异作用控制着弧岩浆的主量和微量元素化学组成，其形成过程是了解弧地壳演化的关键。富含角闪石的堆晶岩，偶尔发现与长英质岩体或变质岩，提供补充的见解弧岩浆分异。在这项研究中，我们进行了岩石学检查的角闪石丰富的超镁铁岩从希达变质杂岩在日本，以更好地了解其作用在弧地壳演化。所研究的样品的特点是大嵌晶角闪石和斜方辉石包围橄榄石颗粒与腐蚀的边缘。角闪石中Cr_2O_3和TiO_2含量较高（分别高达0.9wt%和1.2wt%），轻稀土元素相对于重稀土元素富集。角闪石和橄榄石的显微和地球化学特征表明，角闪石是在地壳深部水化岩浆中以早期结晶的橄榄石（±单斜辉石）为代价形成的，这与经验Al-角闪石压力计估算的结晶压力0.7- 1.0GPa一致。结合希达带中生代深成岩类的母岩浆的弧亲合性和体化学中角闪石分馏的趋势，认为富角闪石深成岩类的形成是作为富角闪石残留物与分异岩浆的互补，对弧壳演化的贡献。
Amphibole controls major and trace element chemistry of arc magma via fractionation, therefore its formation process is the key to understand arc crustal evolution. Amphibole-rich cumulates, occasionally found associated with felsic plutons or metamorphic rocks, provide complementary insights into the arc magma differentiation. In this study, we conducted a petrological examination of amphibole-rich ultramafic rocks from the Hida metamorphic complex in Japan to better understand its role in arc crust evolution. The studied samples are characterized by large poikilitic amphibole and orthopyroxene enclosing olivine grains with corroded margins. Amphibole showed high Cr2O3and TiO2contents (up to 0.9 and 1.2 wt%) and light rare earth element enrichment relative to heavy rare earth elements. Microscopic and geochemical features of amphibole and olivine suggest that the amphibole formed at the expense of early crystalized olivine (± clinopyroxene) from hydrous juvenile magma at a deep crustal level, which is consistent with the estimated crystallization pressure of 0.7–1.0 GPa based on an empirical Al-in-hornblende geobarometer. Considering the arc affinity of parental magma and the amphibole-fractionation trend in bulk chemistry of the Mesozoic plutonic rocks from the Hida Belt, it is implied the formation of amphibole-rich plutonic rocks contributed to arc crustal evolution as amphibole-rich residue complementary to differentiated magma.